Incisor adjustments are widely practiced in some regions on performance horses. This commonly entails reduction of the occusal surface using mechanical burrs with industrial diamond blades and historically diamond cutting wheel. The latter technique, commonly practiced in the USA in the 1990s and subsequently, has been shown to commonly expose incisor occlusal dental pulp and, as well as probably being unnecessary, has a high risk of morbidity and could be considered to be mutilation.

The justification for routinely reducing incisors remains obscure in most cases. Cited reasons include reduction of interlock, improvement of masticatory action, and facilitation of mastication although no convincing objective data has been published to validate these hypotheses. Anecdotally, practitioners claim to have seen no harm resulting from these procedures and claim benefits, that currently appear to be subjective and opinionated.

 Incisor length is maintained constant physiologically between ages 3-15 years1. It is rare that incisor occlusal angles impede molar contact when lateral excursion of the mandible occurs unless previous excessive cheek tooth occlusal reduction has been performed. During prehension of grass the incisors are in occlusion and the cheek teeth which are not masticating, are normally not in occlusion as this is associated with lateral excursion of the mandible.

Incisor malocclusions occur as a result of brachygnathism, class two and three malocclusions and possibly due to uneven attrition due to masticatory pain. Anecdotal terms such as “smile mouth” are usually associated with slight class 2 malocclusion and can become more apparent with age. Evidence that altering incisor occlusal angles has an effect on premolar and molar function is currently lacking, although excessive incisor reduction could result in closer occlusal cheek tooth contact in the absence of excursion, which is not a physiological situation. Incisors have a thicker labial enamel than palatally or lingually, resulting in a labial surface with hight resistance to wear and bending forces and incisors are clinically sensitive especially on the occlusal surfaces. Horses with exposed dental pulp or endodontic disease can show focal pain. In healthy teeth dental pulp can extend to within 1-11 mm of the occlusal surface of the incisors2 and this is normally maintained physiologically. 

Focal adjustment of incisor occlusal angles can help lateral excursion in some cases where it is impeded and can be carefully altered with a burr. Techniques for evaluation of incisor angles have been defined3, and can vary with individual confirmation and change with age. A link between incisor angles and on food prehension and mastication is unclear. Incisor length and angle may be involved in biomechanical changes, that are a risk factor for EOTRH in geriatric horses2. Incisor angle and temporomandibular joint biomechanics have also been described4. However, in many cases incisor reduction appears purely to be performed for cosmetic or commercial benefit, or perceived benefit by owners that is to date unvalidated. Many horses tolerate poorly vibration of instruments on the incisors, and can exhibit pain responses. For this reason, it could be argued that local analgesia should be provided for the majority of incisor treatments.

References
1 Schrock P, Lüpke M, Seifert H, Staszyk C. Three-dimensional anatomy of equine incisors: tooth length, enamel cover and age-related changes. BMC Vet Res. 2013 Dec 9;9:249
2 Englisch, L.M., Rott, P., Lüpke, M., Seifert, H. and Staszyk, C. (2018), Anatomy of equine incisors: Pulp horns and sub-occlusal dentine thickness. Equine Vet J, 50: 854-860.
3 LISTMANN, L. et al. Occlusal Angles of Equine Incisors. Journal of veterinary dentistry, [s. l.], v. 34, n. 4, p. 259–267, 2017.
4 TOMAS RUDOLF STERKENBURGH et al. 2023 Temporomandibular joint biomechanics and equine incisor occlusal plane maintenance. Frontiers in Bioengineering and Biotechnology, 11